The invention relates to an electronic ballast or a gas discharge lamp, particularly but not exclusively for public, security, or amenity applications.
Presently available ballasts generally suffer from a poor power factor, high energy consumption, inflexible control, and large physical weight and size.
There is therefore a need for an improved ballast to overcome these problems.
The invention provides an electronic ballast for a gas discharge lamp, the ballast comprising an input stage DC rectifier, a high frequency invertor connected to load terminals and a control circuit connected to a user interface.
Preferably, the control circuit is programmable. The user interface may receive signals via keys, radio or cellular signal, telephone fixed line, or mains cable. This is particularly useful for setting the lamp to a variety of light setting as desired by operators.
Preferably, the ballast comprises a single inductor for handling both the load high-frequency drive, and lamp ignition. In one embodiment, there is a tap off the drive inductor connected to ground via a capacitor and a switch in series, the switch being controlled by the control circuit to control progressive build up of ignition energy.
In one embodiment, the input stage of the ballast comprises an inductor having primary and secondary windings, whereby the primary windings are used to control charging of a snubbing capacitor and the secondary winding is used to allow discharge of the inductor when charging of the snubbing capacitor is complete and when the switching transistor switches off.
In one embodiment the ballast comprises a capacitor across the lamp terminals and a relay for isolating the capacitor during ignition. Preferably, the control circuit comprises means for controlling the pulse width of gate signals into the invertor switches to control the drive.
In another embodiment the ballast comprises switches for isolating the capacitor during ignition.
According to one aspect of the invention the ballast incorporates a lamp drive circuit.
Preferably the lamp drive circuit incorporates means for synthesis of a low frequency lamp drive waveform. These waveforms may be either square waves or sinusoidal beneficially overcoming incompatibilities with third party discharge lamps. One possible example of these incompatibilities is acoustic resonance of the internal mechanical parts of the lamp which reduces the lamp life.
Ideally the lamp drive circuit is formed for generation of a square wave lamp drive waveform. Beneficially presenting a lower crest factor, being the relationship between peak current and rms current, to further extend lamp life.
In a preferred embodiment the lamp drive waveform has a peak value of less than 1.4 times the root mean square value and in a particulary preferred embodiment the value is 1.1.